Doesn't seems like an issue to me. You would need to inform CIS of the job change citing AC-21 law, along with a letter with similar job desc from your new company (hopefully u have the LC job desc from your previous employer). See numerous posts in AC-21 forum on the same.
U need to file G-28 to change lawyers - pretty straightforward form - ur new lawyer should be able to get it for you.
If you need more answers, please post details of your case like filing date, LC possession, 140 approval, RFE type/date, etc.
Goodluck!
-ab